U.S. Pat. Nos. 5,073,077 and 4,949,079 teach that a digitizer of graphic planar material such as paper may be combined with a touchscreen/stylus sensitive screen by the cooperative use of the the same photodigitizers. This application teaches that the material for digitization need not be restricted to planar material such as paper but can include scenic views, etc.
The difference between the invention taught here and those described in U.S. Pat. Nos. 4,949,079 and 5,073,077 is that this invention employs nonlinear photodetectors, instead of the linear ones employed in those patents. The use of nonlinear photodetectors permits this apparatus to capture three dimensional scenic information. The term nonlinear photodetector used hereafter must be understood to describe the physical shape of the photoreceptive area of the photodetector. It does not refer to the relationship of the output signal strength as a function of input electromagnetic signal.
The invention taught here is significantly different from the one taught by Brown et. al. in U.S. Pat. No. 4,430,526. The invention taught by Brown et.al. uses the tilt of a signal generating stylus to issue commands or instructions regarding modifications to a previously transmitted graphic. It would be inoperative when an inert or passive stylus such as a finger is the means to indicate the desired coordinate. This invention will work with any visible stylus. Also, in this invention, unlike that of Brow, et al, the tilt of the stylus is irrelevant. Finally, the invention of Brown et al, as described in their embodiment, uses the same optical system to image, onto the same photosensitive area of the photodetector, both the stylus (light emitting only) and the graphic material to be scanned. This results in a complex and unwieldy apparatus which requires an optical filter moved by a motor to filter all light except that of the stylus when it is desired to image the stylus.
The present invention also differs from that taught by Japanese Patent 60-138628. That patent teaches how to detect the position of a curser, that is, a projected light spot on a screen. That invention can not indicate the position of a stylus. It would be inoperative with a finger as a coordinate indicator.